1. Field of the Invention
The invention relates to a motor operator for opening or closing contacts of a switchgear adapted for use in mains power distribution systems such as public medium high voltage distribution systems. The motor of the operator may be activated either locally or remotely to open or close the contacts of the switchgear. Alternatively, a drive element normally coupling the motor to the contact operating shaft is selectively removable so that a wrench may be used to manually open and close the contacts in case of failure of the motor operator, or as a safety precaution.
2. Description of the Prior Art
Underground or pole-mounted electrical transmission and distribution systems include a main service line leading from a sub-station with a number of individual distribution lines along the main line connected thereto. It is often the practice, particularly where power is supplied to a user entity such as a discrete residential area, industrial area or shopping area, to provide switchgear in each of the lateral distribution lines connected to the main line in order to enable selective de-energization of the lateral distribution line without the necessity of de-energizing all of the lateral distribution lines. Switchgear conventionally includes electrical, movable contacts which may be opened and closed by maintenance personnel, in case of fault in or maintenance of a distribution line. In a particularly useful type of switchgear, the contacts are mounted under oil or in an inert gas atmosphere.
Generally, the contacts of switchgear require snap action opening and closing mechanisms to minimize arcing and assure a positive closing of the contacts. Actuation of the switch operating mechanism has normally been accomplished manually, requiring service personal to locate and travel to the switchgear in question. Recently, there has been increased interest in switch contact actuating mechanisms that are motor operated and can be activated at remote locations as well as manually locally. In some cases motor operators have been installed within the switchgear cabinet itself for powered actuation of the opening and closing mechanism. By design, these motor operators are not suitable for installation on a retrofit basis on an external side of an existing switchgear cabinet. Moreover, most of the available motor gear operators are relatively expensive, both in terms of cost for various components as well as expenses for installation of the same. Furthermore, these motor operators do not readily lend themselves to manual actuation in the event of motor failure or in the event that the operator desires to open the switch contacts by hand.
As a consequence of the fact that it is almost impossible to incorporate a motor operator in a switchgear cabinet, there is an increased interest in motor operators that can be mounted externally to the cabinet of the switchgear. In this respect it should be noted that it is not allowed to make any holes in the cabinet or make any weldings, which renders the mounting very difficult. It should also be considered that in most cases the motor operator should not only be weather proof but also secured against unauthorized intrusion. Further, it should be fully operable under all weather conditions and operate in a reliable manner.
An example of a motor operator to be mounted externally on a switch gear is dealt with in U.S. Pat. No. 4,804,809. This motor operator may even be mounted as a retrofit unit. The motor operator is composed of an assembly of individual elements mounted in a housing, necessitating a tedious dismounting of the connection between the motor operator and the switchgear for manually operating the switchgear. Further, the motor operator has to be designed for each individual types of switchgear. This renders the motor operator costly. The housing is designed as a regular locker of sheet metal with a door hinged at one side. It should be taken into consideration that the motor operator is located outdoors and subject to dust, rain and snow. The motor operator should operate perfectly under all weather conditions. For safety reasons, the housing should only be accessible to authorized personal and it should be secured against intrusion and vandal proof. In this sense it is fairly easy to get access to a locker.
Hence, there is a need for a motor operator which overcomes these and other problems associated with known devices.